1. Field of the Invention
The present invention relates generally to x-ray tubes and cold electron number amplifiers.
2. Related Art
Many devices require generation of electrons. For example an x-ray tube can include a cathode attached to one end of an evacuated tube and an anode attached at an opposing end. The cathode can include an electron emitter, such as a filament. The filament can be heated, such as by a laser or an alternating current flowing through the filament. Due to the heat of the filament (1500-2000° C. for example) and a very large voltage differential between the filament and the anode (10 kV-100 kV for example) electrons can leave the filament and accelerate towards the anode. The anode can include a material that will emit x-rays in response to impinging electrons. Other examples of devices that require generation of electrons are cathode-ray tubes, electron microscopes, gas electron tubes or gas discharge tubes, and travelling wave tubes.
Electrons in the above devices can be generated by electron emitters, such as a filament. Due to the high required electron emitter temperature for the desired rate of electron emission, the electron emitter can fail at an undesirably low life. For example, in x-ray tubes, filament failure can be one of the most common failures and limiting factors in extending x-ray tube life. It would be desirable to be able to operate electron emitters at a lower temperature than is presently used while maintaining the same electron generation rate.